Electric utility segment - Condensed consolidating statement of income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Condensed Income Statements, Captions [Line Items]
Revenues	$ 661,615	$ 645,874
Expenses
Purchased power	134,000	140,000
Total expenses	583,678	573,985
Total operating income	77,937	71,889
Allowance for equity funds used during construction	2,910	3,294
Retirement defined benefits expense—other than service costs	(763)	(1,833)
Allowance for borrowed funds used during construction	1,078	1,444
Income before income taxes	58,039	53,276
Income taxes	11,878	12,556
Net income	46,161	40,720
Preferred stock dividends of subsidiaries	473	473
Net income for common stock	45,688	40,247
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Revenues	(32)	(42)
Expenses
Fuel oil	0	0
Purchased power	0	0
Other operation and maintenance	0	0
Depreciation	0	0
Taxes, other than income taxes	0	0
Total expenses	0	0
Total operating income	(32)	(42)
Allowance for equity funds used during construction	0	0
Equity in earnings of subsidiaries	(11,849)	(9,325)
Retirement defined benefits expense—other than service costs	0	0
Interest expense and other charges, net	32	42
Allowance for borrowed funds used during construction	0	0
Income before income taxes	(11,849)	(9,325)
Income taxes	0	0
Net income	(11,849)	(9,325)
Preferred stock dividends of subsidiaries	0	0
Net income attributable to Hawaiian Electric	(11,849)	(9,325)
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	(11,849)	(9,325)
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	405,669	401,180
Expenses
Fuel oil	108,922	114,498
Purchased power	105,223	107,370
Other operation and maintenance	81,178	72,940
Depreciation	35,867	34,439
Taxes, other than income taxes	38,631	38,167
Total expenses	369,821	367,414
Total operating income	35,848	33,766
Allowance for equity funds used during construction	2,447	2,887
Equity in earnings of subsidiaries	11,849	9,325
Retirement defined benefits expense—other than service costs	(567)	(1,062)
Interest expense and other charges, net	(12,800)	(12,495)
Allowance for borrowed funds used during construction	902	1,238
Income before income taxes	37,679	33,659
Income taxes	5,283	5,914
Net income	32,396	27,745
Preferred stock dividends of subsidiaries	0	0
Net income attributable to Hawaiian Electric	32,396	27,745
Preferred stock dividends of Hawaiian Electric	270	270
Net income for common stock	32,126	27,475
HELCO | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	87,205	87,933
Expenses
Fuel oil	20,842	18,487
Purchased power	19,177	23,834
Other operation and maintenance	18,736	16,098
Depreciation	10,453	10,055
Taxes, other than income taxes	8,105	8,212
Total expenses	77,313	76,686
Total operating income	9,892	11,247
Allowance for equity funds used during construction	132	111
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	(106)	(103)
Interest expense and other charges, net	(2,901)	(2,907)
Allowance for borrowed funds used during construction	56	64
Income before income taxes	7,073	8,412
Income taxes	1,770	2,177
Net income	5,303	6,235
Preferred stock dividends of subsidiaries	134	134
Net income attributable to Hawaiian Electric	5,169	6,101
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	5,169	6,101
Maui Electric | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	85,653	81,356
Expenses
Fuel oil	30,845	33,983
Purchased power	10,045	8,706
Other operation and maintenance	18,216	18,572
Depreciation	7,627	5,972
Taxes, other than income taxes	8,068	7,725
Total expenses	74,801	74,958
Total operating income	10,852	6,398
Allowance for equity funds used during construction	331	296
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	(30)	(99)
Interest expense and other charges, net	(2,317)	(2,334)
Allowance for borrowed funds used during construction	120	142
Income before income taxes	8,956	4,403
Income taxes	2,181	1,084
Net income	6,775	3,319
Preferred stock dividends of subsidiaries	95	95
Net income attributable to Hawaiian Electric	6,680	3,224
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	6,680	3,224
Other subsidiaries | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	0	0
Expenses
Fuel oil	0	0
Purchased power	0	0
Other operation and maintenance	0	0
Depreciation	0	0
Taxes, other than income taxes	0	0
Total expenses	0	0
Total operating income	0	0
Allowance for equity funds used during construction	0	0
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	0	0
Interest expense and other charges, net	0	0
Allowance for borrowed funds used during construction	0	0
Income before income taxes	0	0
Income taxes	0	0
Net income	0	0
Preferred stock dividends of subsidiaries	0	0
Net income attributable to Hawaiian Electric	0	0
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	0	0
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Income Statements, Captions [Line Items]
Revenues	578,495	570,427
Expenses
Fuel oil	160,609	166,968
Purchased power	134,445	139,910
Other operation and maintenance	118,130	107,610
Depreciation	53,947	50,466
Taxes, other than income taxes	54,804	54,104
Total expenses	521,935	519,058
Total operating income	56,560	51,369
Allowance for equity funds used during construction	2,910	3,294
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	(703)	(1,264)
Interest expense and other charges, net	(17,986)	(17,694)
Allowance for borrowed funds used during construction	1,078	1,444
Income before income taxes	41,859	37,149
Income taxes	9,234	9,175
Net income	32,625	27,974
Preferred stock dividends of subsidiaries	229	229
Net income attributable to Hawaiian Electric	32,396	27,745
Preferred stock dividends of Hawaiian Electric	270	270
Net income for common stock	$ 32,126	$ 27,475